United have been locked in negotiations with Barcelona for weeks, and appear to have finally made a breakthrough.
Transfer expert Fabrizio Romano reports the Red Devils have agreed to pay an initial £56m for the midfielder.
He claims that the "full package" will rise to £74m after add-ons.
ESPN says the exact nature of the performance-based add-ons are yet to be fully agreed.
Personal terms are also still to settled upon, with talks to continue this week.